Sea walls are the most expensive solution, and the only one enabling coastal cities to claim a victory over the sea, however tenuous and temporary. But while Manhattan could feasibly find the money to construct such fortifications, other flood-prone cities might not have the financial wherewithal to construct similar defenses, and may have to resort to strategic accommodation. According to the U.S. Global Change Research Program, coastal cities can either choose to work around the rising water by staying put, elevating parts of the natural and built environment; or beating the retreat as the shoreline inevitably advances inland.
In the Netherlands, which pioneered the expensive sea-wall solution, public debate nevertheless occasionally flares up about giving parts of low-lying wetlands, marshlands and farmlands — won so dearly over the centuries — back to the sea. Rising tides do imply a rising cost of maintaining the status quo.
Nowhere is that lesson more keenly felt than in Venice. Since its founding in the 6th century on an Adriatic archipelago as a refuge from the marauding Ostrogoths and other barbaric invaders, the city whose streets are paved with water has been sinking at an average rate of 1.5 inches per century. But now rising sea levels are combining with the area's naturally soft foundations to accelerate the sinking by as much as five times the previous rate.
The MOSE Project, slated for completion in 2014, is a sea wall similar to the British, Dutch and Russian examples. When finished, it will be able to close off the laguna containing Venice, safeguarding it from high tides. The project is controversial (not to mention expensive, at some 4.7 billion euros), though, and its critics continue to push alternatives, like the scheme to pump the Venetian underground full of sludge to stop the city from subsiding.